cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
Highlighted
Visitor
Visitor
10,356 Views
Registered: ‎10-11-2014

WARNING:Xst:1293 - FF/Latch <n_reg_1> has a constant value of 0 in block <uart_tx_unit>. This FF/Latch will be trimmed during the optimization process.

localparam [1:0]
idle = 2'b00,
start = 2'b01,
data = 2'b10,
stop = 2'b11;
// signal declaration
reg [1:0] state_reg,state_next;
reg [3:0] s_reg,s_next;
reg [2:0] n_reg,n_next;
reg [7:0] b_reg,b_next;
reg tx_reg,tx_next;
 
always @(posedge clk, posedge reset)
if(reset)
begin
state_reg <= idle;
s_reg <= 0;
n_reg <= 0;
b_reg <= 0;
tx_reg <= 1'b1;
end
else
begin
state_reg <= state_next;
s_reg <= s_next;
n_reg <= n_next;
b_reg <= b_next;
tx_reg <= tx_next;
end
initial
begin
n_reg=3'b000;
n_next=3'b000;
end

always @*
begin
state_next = state_reg;
tx_done_tick = 1'b0;
s_next = s_reg;
n_next = n_reg;
b_next = b_reg;
tx_next = tx_reg;
case(state_reg)
idle:
begin
tx_next = 1'b1;
if(tx_start)
begin
state_next = start;
s_next = 0;
b_next = din;
end
end
start:
begin
tx_next = 1'b0;
if(s_tick)
if(s_reg==15)
begin
state_next = data;
s_next = 0;
n_next = 0;
end
else
s_next = s_reg + 1'b1;
end
data&colon;
begin
tx_next = b_reg[0];
if(s_tick)
if(s_reg==15)
begin
s_next = 0;
b_next = b_reg >> 1 ;
if(n_reg==(DBIT-1))
state_next = stop;
else
n_next = n_reg + 1'b1;
end
else
s_next = s_reg + 1'b1;
end
stop:
begin
tx_next = 1'b1;
if(s_tick)
if(s_reg==(SB_TICK-1))
begin
state_next = idle;
tx_done_tick = 1'b1;
end
else
s_next = s_reg + 1'b1;
end
endcase
end
//output
assign tx = tx_reg;
endmodule

 

 

 

 

 

 

how can i remove warnings????

0 Kudos
Reply
5 Replies
Highlighted
Xilinx Employee
Xilinx Employee
10,273 Views
Registered: ‎10-24-2013

Hi,

Please check this AR.

http://www.xilinx.com/support/answers/18397.html

Thanks,Vijay
--------------------------------------------------------------------------------------------
Please mark the post as an answer "Accept as solution" in case it helped resolve your query.
Give kudos in case a post in case it guided to the solution.
0 Kudos
Reply
Highlighted
Historian
Historian
10,257 Views
Registered: ‎02-25-2008

Answered here.

----------------------------Yes, I do this for a living.
0 Kudos
Reply
Highlighted
Visitor
Visitor
4,672 Views
Registered: ‎08-18-2016

@varenyam, have you solved the problem? I have the exact same problem and I still can't get it to work, the block is removed and many signals are not connected even though I have connected those signals in the code, and when I program the FPGA, the transmitter didn't work
0 Kudos
Reply
Highlighted
Moderator
Moderator
4,662 Views
Registered: ‎06-24-2015

@itsna,

 

Did you try the suggestions provided here: https://forums.xilinx.com/t5/Synthesis/Meaning-of-WARNING-Xst-1898-Due-to-constant-pushing/td-p/336971

Thanks,
Nupur
--------------------------------------------------------------------------------------------
Google your question before posting. If someone's post answers your question, mark the post as answer with "Accept as solution". If you see a particularly good and informative post, consider giving it Kudos (click on the 'thumbs-up' button).
0 Kudos
Reply
Highlighted
Moderator
Moderator
4,645 Views
Registered: ‎07-21-2014

@itsna

 

You need to check the design connectivity to make sure warnings are valid or not. First step would be to start from the RTL view and then compare the connections in the generated netlist. 

However, you can preserve cells and nets whenever required, but I would recommend to first analyze the design instead of using attributes.

 

Thanks,
Anusheel
-----------------------------------------------------------------------------------------------
Search for documents/answer records related to your device and tool before posting query on forums.
Search related forums and make sure your query is not repeated.

Please mark the post as an answer "Accept as solution" in case it helps to resolve your query.
Helpful answer -> Give Kudos
-----------------------------------------------------------------------------------------------

 

0 Kudos
Reply